Android的SQLite数据库 - 什么都没有，除了android_metadata [英] android sqlite database - nothing there except android_metadata
问题描述
我有一个小型数据库的Android应用。
我可以使用DA数据库与数据库管理器。
I have an android application with a small database. I can use da database with a database manager.
我尝试了查询，并得到了没有这样的表，所以为了找出哪些表有，我试过，与帮助从这里：
I tried a query and got "no such table", so in order to find out which tables there are, I tried, with help from here:
Cursor c = helper.getReadableDatabase().rawQuery("SELECT name FROM sqlite_master WHERE type=?", new String[] {"table"});
DatabaseUtils.dumpCursor(c);
这样做的结果，但是，是：
The result of this, however , is:
09-22 15:30:59.710: I/System.out(973): >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@b2d5af30
09-22 15:30:59.710: I/System.out(973): >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@b2d5af30
09-22 15:30:59.710: I/System.out(973): 0 {
09-22 15:30:59.720: I/System.out(973): name=android_metadata
09-22 15:30:59.720: I/System.out(973): }
09-22 15:30:59.720: I/System.out(973): <<<<<
我怎样才能找出发生在我的数据库的其余部分。
How can I find out what happened to the rest of my database
我dbhelperclass是：
My dbhelperclass was:
package com.example.myapp;
public class Helper extends SQLiteOpenHelper
{
private static String path = "/data/data/com.example.myapp/databases/";
private static String db = "nn";
private static String dbpath = path + db;
private SQLiteDatabase myDB;
private Context con;
public Helper(Context context) {
super(context, db, null, 1);
this.con = context;
}
public Context getContext(){
return this.con;
}
public void createDataBase() throws IOException{
if(!checkDataBase()){
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
System.out.println("no Database");
}
}
}
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try{
checkDB = SQLiteDatabase.openDatabase(dbpath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
}
if(checkDB != null){
checkDB.close();
return true;
} else {return false;}
}
private void copyDataBase() throws IOException {
InputStream myInput = con.getAssets().open(db);
OutputStream myOutput = new FileOutputStream(dbpath);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
myDB = SQLiteDatabase.openDatabase(dbpath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDB != null)
myDB.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase arg0) {
// TODO Auto-generated method stub
}
@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
// TODO Auto-generated method stub
}
}
我初始化助手这样的：
I initialized the helper thus:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
helper = new Helper(this);
try {
helper.createDataBase();
} catch (IOException ex) {
System.out.println("no start");
}
try {
helper.openDataBase();
} catch (SQLException sqlex) {
System.out.println("does not open");
}
}
好吧原来我得到一个filenotfound异常：
Ok it turns out I get a filenotfound exception:
09-22 18:39:04.103: I/System.out(1119): java.io.FileNotFoundException: /data/data/com.example.myapp/databases/nn
不过：只要我的数据库被命名为NN（它是）和我的应用程序名为MyApp，不应该这样是正确的道路？
nn是的资产。
However: provided my db is named nn (which it is) and my app is named myapp, should not this be the correct path? nn is in assets.
推荐答案
getReadableDatabase（）自动创建一个数据库，不管你在创建初始化的onCreate（）（这是emtpy）。
getReadableDatabase() automatically creates a database, initialized with whatever you create in onCreate() (which is emtpy).
如果您想从数据库中的资源文件夹复制，更好地利用一个已知的工作，如的 SQLiteAssetHelper 。
If you want to copy the database from the assets folder, better use a library that is known to work, such as SQLiteAssetHelper.
这篇关于Android的SQLite数据库 - 什么都没有，除了android_metadata的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
